Explanation/Reference:
Section: Considerations for Expanding an Existing Network Explanation
Explanation:
Cisco recommends Easy Virtual Networking (EVN) with Generic Routing Encapsulation (GRE) tunnels to extend fewer than 32 virtual networks (VNETs) across a WAN. EVN is a network virtualization technique that uses virtual routing and forwarding (VRF) instances to segregate Layer 3 networks. EVN typically uses
802.1Q tagging to extend VNETs across an infrastructure that is within an organization's administrative control, such as a campus LAN. GRE and Multicast GRE (mGRE) tunnels can extend VNETs across an infrastructure that is outside an organization's administrative control, such as a WAN.
EVN supports up to 32 VNETs before operational complexity and management become problematic. Cisco recommends using EVN in small and medium networks? however, implementing a homogeneous EVN topology could require replacing unsupported hardware with EVN-capable devices. Replacing infrastructure is typically disruptive and may require additional modifications to the existing network design.
For small and medium networks needing to extend eight or fewer VNETs across a WAN, Cisco recommends using Multi-VRF, which Cisco also refers to as VRF-Lite. On Cisco platforms, Multi-VRF network virtualization supports up to eight VNETs before operational complexity and management become problematic. Like EVN, Multi-VRF uses VRF instances to segregate a Layer 3 network. The VNETs created by Multi-VRF mirror the physical infrastructure upon which they are built, and most Cisco platforms support Multi-VRF; therefore, the general network design and overall infrastructure do not require disruptive changes in order to support a Multi-VRF overlay topology.
For large networks needing to extend more than 32 VNETs across a WAN, Cisco recommends Multiprotocol Label Switching (MPLS). MPLS is typically implemented in an end-to-end fashion at the network edge and requires the edge and core devices to be MPLS-capable. Integrating MPLS into an existing design and infrastructure can be disruptive, particularly if MPLS-incapable devices must be replaced with MPLS-capable devices at the network edge or in the core. MPLS relies on Multiprotocol Border Gateway Protocol (MPBGP) and Label Distribution Protocol (LDP) to manage the dynamic distribution of VRF information at each Layer 3 device. MPLS is best suited for large networks and can support thousands of VNETs without operational complexity or management becoming problematic.
Reference:
CCDA 200-310 Official Cert Guide, Chapter 4, VRF, p. 154
Cisco: Borderless Campus Network Virtualization-Path Isolation Design Fundamentals: Path Isolation